#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn test_overload() {
        let calc = Calculator {};
        assert!(calc.add(5, 3) == 8);
        assert!(calc.add(5, 3, 2) == 10);
        assert!(calc.add(2.5, 3.5) == 6.0);
    }

}